Resonant piston compressor



Feb. 14, 1967 P. w. CURWEN 3,303,990

RESONANT PISTON COMPRESSOR Filed Feb. 11, 1964 6 Sheets-Sheet 1 43 A /0/ i if 57 a 9 M7 p a jrn/s 7775 02" 9; 2v a; Peter M Curwer) 59 j (TM P. W. CURWEN RESONANT PISTON COMPRESSOR Feb. 14, 1967 6 Sheets-Sheet 3 Filed Feb. 11, 1964 FIG.4.

INVENTOR.

PETER W. CURWEN am 2 CJMZ Feb. 14, 1967 P. w. CURWEN RESONANT PISTON COMPRESSOR 6 Sheets-Sheet 6 Filed Feb. 11, 1964 FI GIO.

FIG.|2.

INVENTOR. PETER W- CURWEN FIG.H.

Feb. 14, 1967 P. w. cuRwEN 3,303,990

RESONANT PISTON COMPRESSOR AUTOMATIC GAIN CONTROL CIRCUIT PREAMPLIFIER POWER TUNED DRIVE PISTON MOTION AMPLIFIER FILTER TRANSDUCER ASSEM' TRANSDUCER Fl-GIB.

INVENTOR.

PETER W. CURWEN Jaw Haw Z M14447 United States Patent 3,303,990 RESONANT PISTGN COMPRESSOR Peter W. Curwen, Burnt Hills, Ballston, N.Y., assignor to Mechanical Technology Incorporated, Latham, N.Y., a corporation of New York Filed Feb. 11, 1964, Ser. No. 344,039 28 Claims. (Cl. 230-55) This application is a continuation-in-part of my copending application similarly entitled Resonant Piston Compressor, Serial No. 232,997, filed October 25, 1962, now Patent No. 3,156,405 and assigned to the same assignee as the present application.

This invention relates to the art of piston compressors and is particularly well adapted for use in satellites, missiles and other terrestrial or celestial space vehicles to supply compressed gas to a gas system. On the one hand the piston compressor may be utilized to supply compressed gas to gas bearing gyroscopes, accelerometers, refrigeration systems, and the like, where a closed gas system is required; on the other hand, however, the compressor may be utilized in open gas systems as represented by such common devices as aquarium air pumps, paint spraying or atomizing devices and the like.

Conventional piston compressors utilize crankshafts, spring loaded valves and other moving parts which place severe limitations on the compressor life and its reliability. These disadvantages result from rubbing contact between the moving parts and create the necessity to lubricate the rotating and reciprocating members with an oil lubricant. In the case of refrigeration compressors, the oil is intimately mixed with the refrigerant used in the system.

To overcome the objections to prior art designs, developmental efforts in recent years led to a design of resonant piston compressor wherein the piston used in compressing the gas is caused to reciprocate by the joint action of a spring and magnetic forces rather than by a motor directly connected to the piston crankshaft. In one well known construction, a movable assembly including pistons and an iron core armature, is carried by springs whose resilient characteristics are so determined that the movable assembly has a natural vibration frequency. To obtain piston actuation in the most efficient manner, the armature connected to the pistons is subjected to the influence of a magnetic field of varying intensity and whose frequency is chosen to correspond with the natural vibration frequency of the movable assembly. When the mechanical and electrical frequencies are the same, a condition of resonance is established in the system.

An important disadvantage of this prior art design and other known resonant piston compressors is that spring loaded valves or deformable portions on the pistons acting as valves, still must be used in controlling the degree of compression of gas in the cylinder compression chamber. They therefore are subject to the same possibilities of failure, and especially wear, as the valving components in the prior art designs preceding them, and thereby adversely affect the compressor reliability to the same extent.

An equally important disadvantage in the prior designs flows from the requirement that the clearance space between the piston skirts and cylinder walls be maintained at the absolute minimum to prevent leakage of the compressed gas from the compression chamber thorugh the clearance space and into the inlet side of the piston. Since the tolerance between these parts is held closely, rubbing contact therebetween occurs, thus necessitating the use of an oil or other liquid type lubricant in the clearance space to minimize wear on the cylinder and piston walls. This not only places a limitation on the compressor life but the compressor cannot be used in those applications requiring operation in oil free environments.

ice

Moreover, because the magnetic core for the winding constitutes a heat sink, temperature changes therein are reflected in'dimension changes in the attached parts, thus disturbing the alignment and causing variation in piston displacement.

In view of the above, it will be apparent the need exists for an improved piston compressor capable of eliminating the above noted deficiencies and the primary object of my invention is therefore directed towards that goal.

Another object of my invention is to provide a piston compressor wherein none of the compressor parts are in rubbing or sliding contact with any other part in the unit.

Still another object of my invention is to provide a gas lubricating film in the clearance space between the piston skirts and cylinder walls for permanently maintaining these parts out of contact with each other.

Another object of my invention is to provide a valving arrangement with no moving parts and utilizing inlet and discharge ports under the control of the compressive element.

Still another object of my invention is the provision of an improved drive arrangement for driving the piston assembly at varying resonant frequencies.

Briefly stated, in accordance with one aspect of my invention, I eliminate the need for grease, oil, or other liquid type lubrication of the piston compressor by excluding all rubbing or sliding contact between the compressor parts. Since relative rubbing contact is eliminated, the piston assembly is maintained in spaced relationship with the cylinder walls during all conditions of operation by a gas which serves both a piston centering and lubricating function. The use of inlet and discharge ports for the gas to be compressed are employed rather than mechanically operating valves heretofore used in compressor constrnctions. Reciprocating motion is imparted to the piston assembly by an improved drive arrangement effective in driving the assembly at different frequencies, depending on whether an open or closed loop circuit is used. In practicing my invention in its broad aspects, it will occur to those skilled in the art that the relationship between the various parts and the disposition of the parts may take various forms and that the principles about to be disclosed are equally applicable to different types of compressor designs.

In the one form of the invention embodied as a double piston compressor and in the other form of the invention embodied as a single piston compressor, the problems in the art are solved and inclusive of its features is the elimination of rubbing and sliding parts concomitant with a minimum of mechanical parts and no wearing surfaces of the parts. And in this connection, a fluid lubricating film is maintained hydrostatically or hydrodynamically, or by a combination hydrostatic-hydrodynamic utilization, in the minimal clearances between the piston skirts and the cylinder walls. It should be appreciated, therefore, that an outstandingly significant feature of this invention resides in the fact that the process gas is the same as the fluid lubricant in the clearance space between the piston and cylinder. This factor allows the invention to be characterized as a single fluid or single phase system because no additional lubrication of any other type, whether solid, liquid or gas, is necessary.

Valves, in the conventional sense are not utilized in either embodiment of the invention. Compression in both embodiments is indirect and is etfectuated internal of the pistons with intake and discharge gas flowing from intake and discharge chambers to the compression area upon registration of respective intake and discharge ports formed through the cylinder walls and pistons.

Drive is imparted to the piston assembly, characterized as the piston-flexure or spring mass system, from drive and control circuitry coupled to the piston assembly and utilizing force and motion transducers. A closed loop, self-oscillating system includes the drive and control circuitry, transducers and piston-fiexure system. Open loop systems includethe drive transducers to drive the piston assembly at line frequency or at double the line frequency. Regardless of the driving system utilized discrete tuning allows the piston assembly to be driven at resonance.

These features and accomplishments and other features and accomplishments should be appreciated from the detailed specification taken in conjunction with the drawings in which like reference numerals refer to similar parts throughout the views, in which:

FIG. 1 is a sectional view of the double piston embodiment of the invention:

FIG. 2 is a sectional view taken along the line 22 of FIG. 1;

FIG. 3 is a block-diagram of the control and drive circuitry;

FIG. 4 is a sectional view of the single piston embodiment of the invention;

FIG. 5 is a view of the piston showing one type of hydrodynamic grooving formed therein;

FIG. 6 is a partial view of the piston showing another type of hydrodynamic grooving formed therein;

FIG. 7 is a partial view of the piston showing another type of hydrodynamic grooving formed therein;

FIG. 8 is a partial view of the piston showing another type of hydrodynamic grooving formed therein;

FIG. 9 is a partial, sectional view of the piston and cylinder showing a hydrodynamic feature;

FIG. 10 is a sectional view taken along the line 1010 of FIG. 4;

FIG. 11 is a circuit diagram for driving the piston assembly at line frequency;

FIG. 12 is a circuit diagram for driving the piston assembly at twice the line frequency;

FIG. 13 is a block-diagram of the control and drive circuitry;

FIG. 14 is an embodiment of a spring that can be substituted for the spring shown in FIG. 4.

Reference numeral 1 generally refers to the invention showing an upper cylinder 3 suitably secured to support structure 5. Arranged intermediate upper cylinder 3 and lower cylinder 7 and suitably secured therewith is cylindri cal spacer 9 of U-shaped configuration in cross-section. Flange 11 formed in the bottom portion of upper cylinder 3 and flange 13 formed in the top portion of lower cylinder 7 receive spacer 9 in abutting relationship therewith.

Received and reciprocable within the cylinders 3 and 7 is double piston comprising an upper piston 15 and a lower piston 17. The piston body 19 of upper piston 15 has formed in the bottom portion thereof a female recess 21 to receive therein a male member 23 formed in the top portion of lower piston body 25 of lower piston 17.

Tails 27 and 29 of the U-shaped spring, rectangular in cross-section, are received in respective complemental slotted openings 31 and 33 formed by the flanges 35 and 37 that extend laterally from their respective upper piston body 19 and lower piston body 25.

As arranged and disposed in the slotted openings 31 and 33, tails 27 and 29 are secured between flanges 35 and 37 by bolts 39 disposed through aligned holes formed in flanges 35 and 37 and tails 27 and 29, with nuts 41 engaged with the threaded portions of bolts 39.

Notwithstanding the flat and U-shaped configuration of spring 43, spring 43 may be of any appropriate configuration provided the spring performs the functions hereinafter described.

Cap screw 45, extending through holes formed in tails 47 and 49 of spring 43, engage tapped holes formed in flange 51 which extends laterally from the bottom portion of lower cylinder 7.

Two slotted openings 53 formed in opposed sides of cylindrical spacer 9 permit free movement of spring 43 therein. 7

The piston assembly, also referred to as the piston flexure or spring mass system, is referred to generally by reference numeral 55 and comprises the pistons 15, 17 and springs 43. Reciprocation or vibration of the piston assembly 55 is etfected by a magnetized or plain iron core 57 of the solenoid or drive transducer 59. Transducer 59 is suitably secured to the internal flange 61 formed in lower cylinder 7. The core 57 is suitably secured to lower piston body 25.

Suitably secured to internal flange 63 formed in upper cylinder 3 is feedback motion transducer 65, also designated as displacement or velocity transducer, with its core 67 suitably secured to upper piston body 19'.

Formed in the upper cylinder 3 are three intake chambers 69 and alternately disposedtherebetween are three discharge chambers 71 with symmetrical arrangement thereall maintained of such disposition.

Formed in lower cylinder 7 are three intake chambers 73 and alternately disposed therebetween are three discharge chambers 75 with symmetrical arrangement thereall maintained of such disposition.

The suitable securement of upper cylinder 3, lower cyl inder 7 and cylindrical spacer 9 is effected by bolts 77 disposed in aligned holes formed through cylinders 3, 7 and spacer 9 with nuts 79 engaged with the threaded portion of bolts 77 as shown.

Suitably secured to upper cylinder 3 and lower cylinder 7 are respective chamber closure rings 81 and 83. Tapped holes are formed laterally adjacent through each of the chamber closure rings 81 and 83 to permit communication internally of chambers 69, 71, 73 and 75 by means of male pipe fittings 85. Disposed externally of the cylinders 3 and 7 is a common intake manifold 87 in communication with the intake chambers 69 and 73 by appropriate piping branches 89 leading from common intake manifold 87.

Disposed externally of cylinders 3 and 7 is a common discharge manifold 91 in communication with discharge chambers 71 and 75 by appropriate piping branches 93 leading from common discharge manifold 91.

In the upper cylinder 3, slotted openings or discharge ports 95 are formed in the top portion of discharge chamber 71 and slotted openings or intake ports 97 are formed in the bottom portion of intake chamber 69; and in the lower cylinder 7, slotted openings or intake ports 99 are formed in the top portion of intake chamber 73 and slotted openings or discharge ports 101 are formed in the bottom portion of discharge chamber 75.

In radial alignment for registration with the slot-ted openings or ports 95, 97, 99 and 101 are respective slotted discharge ports 103 and slotted intake ports 105 formed in the upper piston 15 for communication internally of piston 15, and respective slotted intake ports 107 and slotted discharge ports 109 formed in the lower piston 17 for communication internally of piston 17 Wires 111 lead from feedback motion transducer 65 through grommet 113 to electronic control and drive circuitry. Wires 115 lead from solenoid 59 to the same control and drive circuitry.

Either conventional or specially designed electronic circuits may be utilized with the embodiment of the invention described and shown as long as the operative function described below is obtained; the electronic circuits may utilize either vacuum tube or solid-state circuit elements. The solenoid or drive transducer 59 is connected to and becomes part of the tuned filter circuit 120. The tuned filter circuit is designed to have approximately the same resonant frequency as the piston-flexure-gas system. It should be noted and appreciated that the gas in each one of the compression chambers 117 and 119 exerts a restoring force on their respective pistons 15 and 17 as the gas in these compression chambers 117 and 119 is compressed. The gas hence acts as a pneumatic spring. This pneumatic spring effect along with springs 43 and the mass of the pistons 15 and 17 determine the resonant frequency of the piston assembly 55. Electrical power is supplied to the tuned filter circuit 120 and the drive transducer 59 by the power amplifier 121. The electrical signal from the feedback motion transducer 65, which detects the motion of piston assembly 55, is amplified by the pro-amplifier 122. The electrical signal from pre-amplifier 122 drives power amplifier 121. The piston-flexure system, drive and motion transducers, and electronic drive circuit are thus connected in a closed loop feedback oscillator configuration. When the voltage gain of pre-amplifier is adjusted to a sufliciently high value, selfoscillation of the electro-mechanical system begins and the piston undergoes a reciprocating or vibrating motion at the resonant frequency of the electro-mechanical system. The electrical signal from pro-amplifier 122 also feeds into the automatic gain control circuit 123. The automatic gain control circuit controls the gain of the power amplifier 121 such that the amplitude of the reciprocating or vibrating motion of the piston assembly 55 is maintained at a preselected constant value.

It will be apparent that the closed loop circuit including the components in the block diagram of FIGURE 3 will always drive the piston assembly at the resonant frequency. This condition of operation takes place because the feedback transducer detects the reciprocating frequency of the moving pistons and provides the signal to the pre-amplifier and power amplifier which feed the circuit in tuned filter 120. The filter is designed to provide an output voltage having a frequency the same as that detected by the feedback transducer. When this filter voltage excites the winding in the drive transducer, the force produced by the electro-magnetic circuit is of the same frequency as the vibration frequency of the piston assembly. When this occurs, the piston will drive at the system resonant frequency.

As the load on the piston assembly increases, the pneumatic spring effect provided by the gas of higher pressure in the compression chamber, causes a corresponding increase in the natural vibration frequency of the springpiston mass. When this natural frequency changes, it is detected by the feedback transducer as the iron core 67 connected to the piston reciprocates therein, and the cycle described above is repeated. The system accordingly seeks a new resonant frequency. Obviously, the resonant frequency may vary over a range depending on the particular load being imposed on the piston assembly.

In an open loop circuit, when a power supply of constant frequency is used, such as from a conventional 60 cycle source, the line frequency may not correspond with the natural vibration frequency of the piston assembly when the compressor is under no-load or very light load conditions. However, the piston and springs are initially designed to resonate at the line frequency when full load requirements are placed on the compressor, and when it reaches this normal operating condition, resonance in the system takes place because the mechanical and electrical frequencies will be the same. Nevertheless, the variation from resonance seldom exceeds more than a few percent and as a practical matter, this factor has only slight bearing on the compressor operation.

Radial clearance around the pistons 15 and 17 will be approximately 0.0005 inch to minimize leakage from their respective chambers 117 and 119. The separate common manifolds for each of the intake and discharge ports maintain balanced forces on the piston assembly 55 preventing Wobble or other eccentric movement.

The small leakage of gas provides a hydrostatic gas lubricating film between the piston skirts and the walls of the cylinders which are in telescopic relationship. This film, in addition to very precise manufacturing tolerances held in the facing walls of the pistons and cylinders and symmetry of piston loadings, eliminates actual sliding contact between the piston assembly and the cylinders. Losses attributable to viscous shear between piston assembly and cylinders, and total leakage flow, are negligible in terms of system performance.

Excitation of solenoid 59, sufiice it to say, actuates the reciprocation or vibration of the piston assembly 55 with downward movement placing a compressive force on springs 43 and upward movement placing the springs 43 under tension.

When ports 105, upon downward movement, are in communication with openings 97, gas will be drawn into chamber 117 as a result of the partial vacuum in chamber 117. Further downward movement of piston assembly 55 will permit ports 109 to communicate with openings 101 and release the compressed gas trapped in chamber 119.

Upward movement of piston assembly 55 first relieves the compressive force upon spring 43 and further upward movement places the spring 43 under tension. When ports 107, upon upward movement are in communication with openings 99, gas will be drawn into chamber 119 as a result of the partial vacuum in chamber 119. Further upward movement of the piston assembly 55 will permit ports 103 to communicate with openings and release the compressed gas trapped in chamber 117.

In FIG. 4, reference numeral 121 refers generally to the invention embodied as a single piston compressor. Mounting of the compressor assembly for a minimum of vibration during operation of the compressor is effectuated by indirect spring mounting of the compressor with respect to support structure 123. Four upstanding posts 125 are fixed to support structure 123. Each of the upstanding mounting posts 125 carries at its upper portion a laterally arranged and disposed spring post 127. Cylinder 129 carries at its bottom portion four spring posts 131 laterally extending therefrom. Each tension spring 133 has tails 135 carried by spring posts 127 and 131. Suitably secured to the upper portion of the cylinder 129 is a support plate 137 carrying the drive transducer generally referred to by reference numeral 139. Disposed in a removed portion 141 of the support structure 123 is a support plate 143 fixed to the cylinder head 145 by cap screws 147 and fixed to the cylinder 129 by cap screw 149. Support plate 143 carries the feedback motion transducer 151.

Disposed as shown within the cylinder wall 153 is the piston 155 having fixed internal thereof a cross plate or piston head 157 fixed upon which is the piston rod 159. Suitably attached to piston rod 159 is the core 161 of drive transducer 139. Piston rod 159 has formed at its upper portion a shoulder flange 163 against which in abutting relationship is emplaced lower mounting plate 165. Upper mounting plate 167 is formed with removed portions 16-9 in which the upper terminal portions 171 of the four, symmetrically arranged and disposed fiat springs 173 of U-shaped configuration are received. Cap screws 175 inserted through aligned holes formed in the upper mounting plate 167 and the upper terminal portions 171 of the springs 173 secure springs 173 therewith by engagement of cap screws 175 with tapped holes formed in lower mounting plate 165. Piston rod 159 has a threaded portion 177 with which is engaged the nut 179. Nut 179 sufficiently tightened upon the threaded portion effects clamped securement of lower mounting plate 165 with shoulder flange 163.

Mounting plate 181 has removed portions 183 in which are received the lower terminal portions 185 of U-shaped springs 173. Cap screws 137 inserted through aligned holes formed in mounting plate 181 and the lower terminal portions 185 of springs 173 are engaged with tapped holes formed in the cylinder head 145. Disposed intermediate mounting plate 181 and support plate 143 is the spacer plate 189. Aligned holes formed in support plate 143, spacer plate 189 and mounting plate 181 permit the insertion therethrough of cap screw 147 and engagement with the tapped hole formed in cylinder head 145.

Tapped holes 191 and 193 formed in the cylinder 129 permit external communication with the annular intake and discharge chambers 195 and 197, respectively, formed in the cylinder 129. Male pipe fitting may be engaged with tapped holes 191 and 193 to effect communication therewith. Annular intake and discharge grooves 199 and 201 are formed in the cylinder wall 153 and are in common communication, as shown, with intake and discharge chambers 195 and 197, respectively. A plurality of symmetrically arranged intake and discharge slotted openings or ports 203 and 205 are formed in the cylinder wall 153 and are in communication with intake and discharge grooves 199 and 201, respectively. Thus, internal communication of cylinder wall 153 is permitted in the intake line from tapped hole 191, intake chamber 195, intake groove 199 to ports 203; and from the interior of cylinder wall 153 to the discharge line through ports 205, discharge groove 201, discharge chamber 197 to tapped hole 193.

In radial alignment for registration upon reciprocation or vibration of piston 155 with either the intake slotted openings or ports 203, or the discharge slotted openings or ports 205, are slotted openings or ports 207 formed through piston 155. Thus upon reciprocation or vibration of piston 155, ports 207 register alternately with ports 205 and 207 for establishment of communication internally of piston 155 by the respective intake and discharge lines.

In the upward intake or return stroke of piston 155 and upon registration of ports 207 with ports 203, gas will be drawn into the compression chamber 209 through the intake line because of the partial vacuum that exists in compression chamber 209. In the downward discharge or compression stroke of piston 155 the gas trapped in the compression chamber 209 will be compressed and upon registration of ports 207 with ports 205, gas will flow from the compression chamber 209 through the discharge line. Reference numeral 211 indicates the deflected position of springs 173 in such discharge stroke and reference numeral 213 indicates the lowermost position of piston 155 in its discharge stroke.

Hydrostatic gas lines 215 formed in the cylinder 129 communicate with the tapped hole 193 and annular grooves 217 formed in the cylinder 129. Formed in the cylinder wall 153 are feeder holes 219 communicating with grooves 217 and a plurality of orifices 221 formed in cylinder wall 153, and in symmetrical arrangement and disposition therearound. Plug 223 is engaged in a tapped hole formed in the cylinder 129, as shown.

Upon registration of ports 207 with ports 205 the compressed gas will be discharged through the discharge line. A portion of the discharging compressed gas will bleed through the hydrostatic gas lines 215 through annular grooves 217 and feeder holes 219 and through orifices 221 to the internal portion of cylinder wall 153 to provide gas lubrication in the small radial clearance space maintained between the exterior of piston 155 and the interior of cylinder wall 153. A plurality of holes 225 formed in the cylinder wall 153 are symmetrically arranged and disposed therein. Holes 225 communicate with annular grooves 227 and 229 formed in the interior and exterior of cylinder wall 153. A vent 231 formed in the cylinder 129 communicates with groove 229 and allows the hydrostatic gas to be vented to atmosphere. This hydrostatic gas also vents to atmosphere at the bottom 233 of cylinder wall 153 and from the top 235 of cylinder wall 153.

It should be clearly understood and appreciated that the hydrodynamic structure hereinafter described for piston 155 in FIGS. 5, 6, 7, 8 and 9, can be utilized for pistons 15 and 17 of the double piston compressor previously described with reference to FIGS. 1, 2 and 3 herein. Although the double piston compressor provides for a hydrostatic gas lubricating film between the piston skirts and the walls of the cylinders, the hydrostatic gas lubricating structure embodied in the hydrostatic gas lines 215, annular grooves 217, 227 and 229, feeder holes 219, orifices 221 and holes 225 and vent 231 may be appropriately incorporated in the double piston compressor. Furthermore, it should also be appreciated that the combination hydrostaticd'iydrodynamic structure as hereinafter described with reference to the single piston compressor may likewise be incorporated in the double piston compressor, and that such combination of hydrostatichydrodynamic function and feature would have utility in other structures separate and apart from that disclosed herein.

In FIG. 5, two staggered rows of helical grooves 237 and 239, of shallow depth, are formed in the upper skirt of piston and two staggered rows of helical grooves 241 and 243, of shallow depth, are formed in the lower skirt of piston 155. A manifold 245 formed in piston 155 as a continuous groove communicates with helical grooves 239, and a manifold 247 for-med in piston 155 as a continuous groove communicates with helical grooves 241. Helical grooves 237, 239, 241 and 243 are symmetrically arranged and disposed on piston 155.

In FIG. 6, pockets 249, of shallow depth, are formed in the lower skirt of piston 155. The pockets 249 are of rectangular configuration, and are symmetrically arranged and disposed on the lower skirt of piston 155. Similar arrangement and disposition of pockets 249 is made on the upper skirt of piston 155. Pockets 155 may also be tapered or stepped, and inclusively may be of a configuration other than rectangular.

In FIG. 7, two rows of pockets 251 and 253, of shallow depth, are formed in the lower skirt of piston 155. Pockets 251 communicate with a manifold 255 for-med in piston 155 as a continuous groove. The pockets 251 and 253 are of rectangular configuration, and are symmetrically arranged and disposed on the lower skirt of piston 155. Similar arrangement and disposition of pockets 251 and 253, and manifold 255 is made on the upper skirt of piston 155. Pockets 251 and 253 may also be tapered or stepped, and inclusively may be of a configuration other than rectangular.

In FIG. 8, a row of helical grooves 257, of shallow depth, is formed in the lower skirt of piston 155. Helical grooves 257 are symmetrically arranged and disposed on the lower skirt of piston 155. Similar arrangement and disposition of helical grooves 257 is made on the upper skirt of piston 155.

It should be noted, however, that the sense of grooves 241 and 243 can be opposite from the sense of grooves 237 and 239; and that the sense of grooves 257 in the lower skirt of piston 155 can be opposite from the sense of grooves 257 formed in the upper skirt of piston 155. Furthermore, grooves 237, 239, 241, 243 and 257 in crosssection may be either of square shape, rectangular shape, or semicircular shape. Opposite sense of the grooves is utilized to balance or cancel tangential force components arising upon reciprocation of the piston.

In FIG. 9, the lower skirt of piston 155 is tapered inwardly at 259, as shown. The upper skirt of piston 155 is similarly tapered inwardly, but in an opposite sense.

The reciprocation or vibration of piston 155 in cylinder wall 153 may be compared functionally to the attributes of the movement of a journal relative to its bearing, respectively. In FIGS. 5-9, the configurations of the upper and lower skirts in the forms of helical grooves, pockets or tapering, effect a shearing of the gas in the minimal radial clearance between the piston and cylinder wall. This shearing of the gas generates positive pressure buildup of the gas independent and apart from compression of the gas taking place in the compression chamber 209. Accordingly, ambient gas will be induced to flow into the minimal radial clearance space between the interior of the cylinder wall 153 and exterior of the piston 155. This self-acting feature of the piston of the generation of positive pressure in the radial clearance space upon reciproca- 9 tion or vibration of the piston 155 provides for stability of the piston 155 and for a lubricating pressurized gas film between the piston and cylinder wall.

The fact of the minimal clearance space between the interior of the cylinder wall 153 and the exterior of the piston 155 of the single piston compressor is characterized as a telescopic relationship with respect to all the embodiments of the invention as heretofore described.

When the hydrostatic feature, as previously described, is combined with the hydrodynamic feature, as previously described, the overall effect will be the maintenance of a lubricating gas film under pressure in the minimal, radial clearance space between the interior of the cylinder wall 153 and the exterior of the piston 155. This lubricating pressurized gas film will be maintained longitudinally along the interior of the cylinder wall 153 and the exterior of the piston 155 regardless of the position of piston stroke during the cycle.

The piston assembly, also referred to as the pistonflexure or spring mass system, comprises the piston 155 and U-shaped springs 173. Reciprocation or vibration of the piston assembly is eifectuated byexcitation of drive transducer 139. The solid line position of springs 173 in FIG. 4 is the position of springs 173 whereat springs 173 are under maximum tension. Dotted line position 211 of springs 173 whereat the springs 173 are placed under maximum compression. The equilibrium position of springs 173 occurs when port 207 is midway between intake port 203 and discharge port 205. When gas trapped in compression chamber 209 is being compressed, the springs 173 are being placed under increasing compression. This compressed gas acts as a pneumatic spring, and this pneumatic spring effect along with springs 173 and the mass of piston 155 determine the resonant frequency of the piston assembly.

In FIG. 11 the coil 265 of the drive transducer 139 is connected in the circuit 261 as shown, and wherein a rectifier 263 in series with coil 265 is connected across the alternating current source 267. By tuning the fundamental frequency of the piston fiexure system to essentially the line frequency of the alternating current source, the piston assembly will resonate at the line frequency.

In FIG. 12 the coil 265 at the drive transducer 139 is connected in the circuit 269 as shown, and wherein the coil 265, is connected across the alternating current source 267. In this open loop configuration the piston assembly will reciprocate or vibrate at twice the line frequency when the piston assembly is discretely tuned such that its fundamental frequency is approximately twice the line frequency.

In the open loop configuration shown in FIGS. 11 and 12, the feedback motion transducer 151 is not utilized.

In the closed loop feedback oscillator configuration shown in FIG. 13, the electronic circuit may employ either vacuum tube or solid-state circuit elements. The piston assembly comprising the piston 155 and U-shaped springs 173 are designated by reference numeral 275 for easier reference. Drive transducer 139 is connected to and becomes part of the tuned filter circuit 277 which is designed to have approximately the same resonant frequency as the piston assembly 275. Electrical power is supplied to the tuned filter circuit 277 and drive transducer 139 by the power amplifier 279. The electrical signal from the feedback motion transducer 151, which detects the motion of piston assembly 275, is amplified by the preamplifier 281. This electronic signal from pre-amplifier 281 drives power amplifier 279. The piston assembly 275, drive and motion transducers 139 and 151, and the electronic drive circuit are thus connected in a closed loop feedback oscillator configuration. When the voltage gain of pre-arn-plifier 281 is adjusted to a sufficiently high value, self-oscillation of the electromechanical system begins and piston 155 undergoes a reciprocating or vibrating motion at the resonant frequency of the electromechanical system. The electrical signal from pre-amplifier 281 also feed into the automatic gain control circuit 283 which controls the gain of the power amplifier 279 such that the amplitude of the reciprocating or vibrating motion of the piston assembly 275 is maintained at a pre-selected constant value. Thus the piston assembly 275 is always driven at the fundamental resonant frequency of the electromechanical system regardless of shifts in this resonant frequency caused by temperature or aging effects on the component parts of the system.

The cooperative arrangement and association of the helical coil spring 285 may be utilized as a substitute for the four U-shaped springs 173. Coil spring 285 is carried by an upstanding shoulder 287 formed on cylinder head 145 and a depending shoulder 289 formed on cross plate or piston head 157. Coil spring 285 functions as do the four U-shaped springs 173 function. Spring 285 is placed under compression and tension in a manner similar to the compression and tension forces acting upon springs 173.

In the embodiments heretofore described of the double piston compressor and the single piston compressor, the phenomenon of the compression in cooperative association and interrelationship with the described structure may be referred to as indirect compression. In conventional piston-cylinder structures, moreover, the compression occurs by a piston head on the exterior of a piston acting upon trapped gas in a cylinder having a cylinder head at one end of the cylinder. Upon movement of the piston head toward the cylinder head and decrease in distance between the two, the pressure of the trapped gas acted upon or compressed rises. In the embodiments heretofore described compression takes place not within a cylinder compression chamber, but in a piston compression chamber. Intake and discharge of the gas occurs not from the cylinder but from the piston. And the cylinder head is not at the end of the cylinder but is disposed interior of the piston with the piston head being disposed not at the end of the piston but intermediate the interior of the piston.

The terminology upper cylinder head and lower cylinder head as used in the claims is with reference to the double piston compressor embodied in FIGS. 1, 2 and 3. The lower cylinder head is the housing structure secured to internal flanges 61 formed in lower cylinder '7, and this housing structure houses the drive transducer 59. The upper cylinder head is the housing structure secured to internal flange 63 formed in upper cylinder 3, and this housing structure houses the feedback motion transducer 65. Likewise the terminology upper piston head refers to the horizontal disposed portion of piston body 19, and which horizontally disposed portion is integral with the piston body 19 and piston skirt of upper piston 15; and the terminology lower piston head refers to the horizontally disposed portion of lower piston body 25, and which horizontally disposed portion is integral with lower piston body 25 and the piston skirt of lower piston 1'7. And the terminology biasing means refers to the springs 43 of the double piston compressor, or refers to the springs 173 or 285 of the single piston compressor.

It should be noted that the transducers 59, 65, 139 and 151 are of the conventional type and whose functional attribute is the conversion of mechanical to electrical energy, or vice-versa. In the drive transducers 59 and 139 the structural components are those of conventional solenoids. In the drive transducers 59 and 139, the electrical input power is converted to mechanical power to drive their respective piston assemblies. In the feedback motion transducers 65 and 151, an electrical signal is produced proportional to either the displacement, the velocity, or the acceleration, of the driven system. In transducer 65, magnetic lines of force are cut by magnetic core 67 to induce a voltage in the windings of transducer 65. In transducer 151, a variable reluctance pickup may be utilized in embodiment to effectuate voltage inducement. Other types of conventional transducers which accomplish the discrete conversions as delineated may be substituted for the transducers herein.

Having thusly described my invention, I claim:

1. A resonant piston compressor comprising, a piston assembly consisting of biasing means and a piston, a cylinder housing said piston, intake and discharge ports in said cylinder for supplying gas for compression and subsequent delivery to a point of use, said cylinder further having inlet and discharge chambers respectively communicating with said intake and discharge port-s, said biasing means connected at one end to a stationary member and at its other end to said piston, drive means coupled with said piston assembly, the arrangement being such that the separate forces imparted to said piston by the drive means and biasing means causes it to reciprocate in said cylinder at a resonant frequency, and fluid lubricating means comprising gas under pressure in the clearance space between said piston and cylinder.

2. The subject matter as claimed in claim 1, wherein said fluid lubricating means comprising the coacting side wall surfaces of said piston and cylinder and hydrostatic gas lines interconnecting said discharge chamber and said clearance space for bleeding pressurized gas.

3. The subject matter as claimed in claim 2, wherein orifices extend through the cylinder wall of said cylinder and wherein said orifices communicate with said hydrostatic gas lines.

4. The subject matter as claimed in claim 1, wherein said fluid lubricating means comprises the coacting side wall surfaces of said piston and cylinder for developing a gas under positive pressure in said clearance space generated by said piston shearing the gas upon reciprocation or vibration of said piston.

5. The subject matter as claimed in claim 4, wherein said piston has skirts and wherein said skirts have formed therein shallow depth helical grooves for shearing the gas.

6. The subject matter as claimed in claim 5, wherein said helical grooves formed in one of said skirts are in opposite sense to said helical grooves formed in the other one of said skirts.

7. The subject matter as claimed in claim 4, wherein said piston has skirts and wherein said skirts have formed therein staggered rows of shallow depth helical grooves for shearing the gas.

8. The subject matter as claimed in claim 7, wherein said staggered rows of helical grooves formed in one of said skirts are of one sense and wherein said staggered rows of helical grooves formed in the other one of said skirts are of an opposite sense.

9. The subject matter as claimed in claim 8, wherein said piston has manifolds formed therein, and wherein one of said manifolds communicates with one of said staggered rows formed in one of said skirts of one sense, and wherein the other one of said manifolds communicates with one of said staggered rows formed in the other one of said skirts of opposite sense.

10. The subject matter as claimed in claim 4, wherein said piston has skirts and wherein said skirts have formed therein shallow depth pockets for shearing the gas.

11. The subject matter as claimed in claim 10, wherein said pockets are tapered.

12. The subject matter as claimed in claim 10, wherein said pockets are stepped.

13. The subject matter as claimed in claim 4, wherein said piston has skirts and wherein said skirts have formed therein rows of shallow depth pockets for shearing the gas.

14. The subject matter as claimed in claim 13, wherein said piston has manifolds formed therein and wherein one of said manifolds communicates with one of said rows of pockets formed in one of said piston skirts andthe other one of said manifolds communicates with one of said rows of pockets formed in the other one of said piston skirts.

15. The subject matter as claimed in claim 4, wherein said piston has skirts and wherein said skirts are tapered inwardly for shearing the gas.

16. The subject matter as claimed in claim 1, wherein said fluid lubricating means comprise hydrostatic gas lines interconnecting said discharge chamber with said clearance space for bleeding pressurized gas therebetween, and gas of positive pressure in said clearance space generated by said piston shearing the gas upon reciprocation or vibration of said piston.

17. In a device comprising two members having a clearance space therebetween and cyclically compressing and discharging pressurized gas produced upon relative motion of said members, a fluid lubricating means of gas under pressure in said clearance space, said fluid lubricating means comprising hydrostatic gas lines bleeding a portion of the discharge of the pressurized gas produced and supplying same to said clearance space, and gas of positive pressure in said clearance space generated by one of said members shearing the gas in said clearance space upon relative movement of said members.

18. A resonant piston compressor for compressing gas and supplying same to a gas system, said resonant piston compressor comprising a piston assembly, a cylinder, drive means and fluid lubricating means; said piston assembly being coupled to said drive means to drive said piston assembly at resonance, said piston assembly comprising a piston and biasing means for biasing said piston, said piston being biased upon movement of said piston from its equilibrium position, said piston being received and reciprocable within said cylinder, said cylinder having a cylinder head, said cylinder head being disposed interiorly of said piston, said piston having skirts and a piston head interiorly disposed, said piston head, cylinder head and interior of one of said skirts forming a compression chamber for indirect compression of the gas, said cylinder having intake and discharge ports in common with respective intake and discharge chambers, said piston having ports, said piston ports alternately registering with said cylinder intake and discharge ports to establish communication with said compression chambers upon reciprocation or vibration of said piston assembly, said cylinder having a wall, the interior of said cylinder wall and the exterior of said piston having a clearance space, and said fluid lubricating means comprising gas under pressure in said clearance space provided between said piston and cylinder.

19. The subject matter as claimed in claim 18, wherein said drive means comprise a drive transducer operatively connected to said piston assembly to drive said piston assembly at its resonant frequency.

20. The subject matter as claimed in claim 18, wherein said drive means comprise a drive transducer operatively connected to said piston assembly to drive said piston assembly and a feedback motion transducer positioned to detect motion of said piston assembly to thereby drive said piston assembly at its resonant frequency.

21. The subject matter as claimed in claim 18, wherein said biasing means comprise U-shaped springs operatively connected to said piston and cylinder.

22. The subject matter as claimed in claim 18, wherein said fluid lubricating means comprise hydrostatic gas lines bleeding pressurized gas from said cylinder discharge chamber and supplying same to said clearance space through orifices formed through said cylinder wall in communication with said hydrostatic gas lines.

23. The subject matter as claimed in claim 18, wherein said piston has gas shearing means and wherein said fluid lubricating means comprise gas of positive pressure in said clearance space generated hydrodynamically by said piston shearing means shearing the gas upon reciprocation or vibration of said piston.

24. The subject matter as claimed in claim 18, wherein said piston has gas shearing means, wherein said fluid lubricating means comprise hydrostatic gas lines bleeding pressurized gas from said cylinder discharge chamber and supplying same through said hydrostatic gas lines and through communicating orifices formed through said cylinder wall, and gas of positive pressure in said clearance space generated hydrodynamically by said piston shearing 13 means shearing the gas upon reciprocation or vibration of said piston.

25. The subject matter as claimed in claim 24, wherein support structure is further provided upon which to mount said resonant piston compressor and wherein indirect spring mounting means is provided to mount said resonant piston compressor upon said support structure for a minimum of vibration of said resonant piston compressor during its operation, said indirect spring mounting means comprising upstanding mounting posts, spring posts, cylinder spring posts and tension springs; said upstanding mounting posts being fixed to said support structure, each of said upstanding mounting posts carrying a spring post, said cylinder carrying said cylinder spring posts, one of said tension springs being carried by and between one of said spring posts and one of said cylinder spring posts.

26. A resonant piston compressor for compressing gas and supplying same to a gas system, said resonant piston compressor assembly comprising a piston assembly, upper and lower cylinders and drive means; said piston assembly being coupled to said drive means to drive said piston assembly at resonance, said piston assembly comprising an upper piston, a lower piston and biasing means, said biasing means being operatively connected to one of said pistons and one of said cylinders, said pistons being received and reciprocable within their respective cylinders, said pistons being biased by said biasing means upon movement of said pistons from their equilibrium position, each of said cylinders having a cylinder head, said cylinder heads being disposed interiorly of their respective pistons, each of said pistons having skirts and a piston head interiorly disposed, each of said respective piston heads, cylinder heads and piston skirt interiors forming separate compression chambers for indirect compression of the gas trapped therein, each of said cylinders having intake and discharge ports, each of said cylinders having intake and discharge chambers, each of said cylinder intake and discharge ports being in common with each of said cylinder intake and discharge chambers, respectively, each of said piston intake and discharge ports alternately registering with each of said cylinder intake and discharge ports, respectively, to establish communication with each of said compression chambers, respectively, upon reciprocation or vibration of said piston assembly, a wall forming each of said cylinders, the interior of each cylinder wall and the exterior of each piston forming a clearance space there between, and fluid lubricating means associated with each of said clearance spaces for accommodating a lubricating gas under pressure, said fluid lubricating means comprising orifices formed in each of said cylinder walls, and hydrostatic gas lines interconnecting each of said cylinder discharge chambers and said clearance spaces for bleeding pressurized gas from said discharge chambers through said orifices to said clearance spaces for providing a lubricating gas film in the said clearance spaces.

27. A resonant piston compressor for compressing gas and supplying same to a gas system, said resonant piston compressor assembly comprising a piston assembly, upper and lower cylinders and drive means; said piston assembly being coupled to said drive means to drive said piston assembly at resonance, said piston assembly comprisiing an upper piston, a lower piston and biasing means, said biasing means being operatively connected to one of said pistons and one of said cylinders, said pistons being received and reciprocable within their respective cylinders, said pistons being biased by said biasing means upon movement of said pistons from their equilibrium position, each of said cylinders having a cylinder head, said cylinder heads being disposed interiorly of their respective pistons, each of said pistons having skirts and a piston head interiorly disposed, each of said respective piston heads, cylinder heads and piston skirt interiors forming separate compression chambers for indirect compression of the gas trapped therein, each of said cylinders having intake and discharge ports, each of said cylinders having intake and discharge chambers, each of said cylinder intake and discharge ports being in common with each of said cylinder intake and discharge chambers, respectively, each of said piston intake and discharge ports alternately registering with each of said cylinder intake and discharge ports, respectively, to establish communication with each of said compression chambers, respectively, upon reciprocation or vibration of said piston assembly, a wall forming each of said cylinders, the interior of each cylinder wall and the exterior of each piston forming a clearance space there between, and fluid lubricating means associated with each of said clearance spaces for accommodating a lubricating gas under pressure, said fluid lubricating means comprising gas shearing means on each of said pistons for hydrodynamically generating a gas of positive pressure in said clearance spaces upon reciprocation or vibration of said pistons.

28. A resonant piston compressor for compressing gas and supplying same to a gas system, said resonant piston compressor assembly comprising a piston assembly, upper and lower cylinders and drive means; said piston assembly being coupled to said drive means to drive said piston assembly at resonance, said piston assembly comprising an upper piston, a lower piston and biasing means, said biasing means being operatively connected to one of said pistons and one of said cylinders, said pistons being received and reciprocable within their respective cylinders, said pistons being biased by said biasing means upon movement of said pistons from their equilibrium position, each of said cylinders having a cylinder head, said cylinder heads being disposed interiorly of their respective pistons, each of said pistons having skirts and a piston head interiorly disposed, each of said respective piston heads, cylinder heads and piston skirt interiors forming separate compression chambers for indirect compression of the gas trapped therein, each of said cylinders having intake and discharge ports, each of said cylinders having intake and discharge chambers, each of said cylinder intake and discharge ports being in common with each of said cylinder intake and discharge chambers, respectively, each of said piston intake and discharge ports alternately registering with each of said cylinder intake and discharge ports, respectively, to establish communication with each of said compression chambers, respectively, upon reciprocation or vibration of said piston assembly, a wall forming each of said cylinders, the interior of each cylinder wall and the exterior of each piston forming a clearance space there between, and fluid lubricating means associated with each of said clearance spaces for accommodating a lubricating gas under pressure, said fluid lubricating means comprising hydrostatic gas lines interconnecting each of said cylinder discharge chambers and said clearance spaces for supplying pressurized gas from said chambers through orifices in said cylinder walls and into said clearance spaces, and gas shearing means on each of said pistons for generating a gas of positive pressure in each of said clearance spaces when each of said pistons reciprocate or vibrate in said cylinders.

References Cited by the Examiner UNITED STATES PATENTS 2,721,024 10/1955 Zeh 23055 2,722,891 11/ 1955 Weinfurt 103-5 3 2,907,304 10/1959 Macks 92-153 X 2,935,672 5/1960 Ross 3l8128 2,983,098 5/1961 Bush 3089 X 2,988,684 6/ 1961 Rijckaert 318-128 3,007,625 11/1961 Dolz 23055 3,043,635 7/1962 Bard 308-9 3,093,301 6/ 1963 Mitchell 230206 3,105,631 10/1963 Hanny 230-116 3,128,941 4/1964 Waibel 230-206 ROBERT M. WALKER, Primary Examiner. 

1. A RESONANT PISTON COMPRESSOR COMPRISING, A PISTON ASSEMBLY CONSISTING OF BIASING MEANS AND A PISTON, A CYLINDER HOUSING SAID PISTON, INTAKE AND DISCHARGE PORTS IN SAID CYLINDER FOR SUPPLYING GAS FOR COMPRESSION AND SUBSEQUENT DELIVERY TO A POINT OF USE, SAID CYLINDER FURTHER HAVING INLET AND DISCHARGE CHAMBERS RESPECTIVELY COMMUNICATING WITH SAID INTAKE AND DISCHARGE PORTS, SAID BIASING MEANS CONNECTED AT ONE END TO A STATIONARY MEMBER AND AT ITS OTHER END TO SAID PISTON, DRIVE MEANS COUPLED WITH SAID PISTON ASSEMBLY, THE ARRANGEMENT BEING SUCH THAT THE SEPARATE FORCES IMPARTED TO SAID PISTON BY THE DRIVE MEANS AND BIASING MEANS CAUSES IT TO RECIPROCATE IN SAID CYLINDER AT A RESONANT FREQUENCY, AND FLUID LUBRICATING MEANS COMPRISING GAS UNDER PRESSURE IN THE CLEARANCE SPACED BETWEEN SAID PISTON AND CYLINDER. 